1. Field of the Invention
The present invention relates to a gas-filled discharge tube, and more particularly to a gas-filled discharge tube for operation as a series gap of an ignition system of an automotive spark-ignition engine or the like.
2. Description of the Prior Art
There has been proposed a conventional gas-filled discharge tube for operation as a series gap of an ignition system of an automotive spark-ignition engine or the like. One such conventional tube is disclosed by the same applicant as the present specification; Japanese Utility Model Laid-open No. 1-82245.
FIG. 6 shows a conventional gas-filled electric discharge tube 1 as noted above, wherein at the opposite open ends of a tubular body 2 formed of an electrically insulating material such as ceramic. There are formed a pair of electrode bases 4a and 4b airtightly adhered to the respective open ends for installing electrodes 3a and 3b as discharge electrodes. These electrodes are formed by pressing a porous metal sheet on the respective electrode bases 4a and 4b, and to this structure, a gas-filled tube 5 is airtightly mounted on one electrode base 4a. A connecting portion 6 (which is explained later on) is protrudingly formed on the other electrode base 4b. With this construction, a gas-filled discharge tube 1 is formed such that a high-pressurized inert gas is injected into the tubular body 2 from the gas-filled tube 5. After the completion of the gas injection, the tube 5 is sealed by a gas sealing member 7, and thereafter a cylindrical shaped protection terminal 8 is provided to cover the external side of the tube 5. An electrically conducting adhesive member 9 is filled between the protection terminal 8 and the tube 5.
The gas-filled discharge tube 1 as constructed above as shown in FIG. 7, is incorporated into a plug gap 10 which is to be engaged with a terminal of the spark plug. A pair of intermediate connecting terminals 14, 14, are formed respectively at one end of the connecting terminal 11 and at one end of a cable terminal 13 connected to an end portion of a high-voltage cable 12, and are engageably fixed respectively with the protection terminal 8 of the electrode base 4a and the connecting portion 6 of the electrode base 4b of the gas-filled discharge tube 1. A so-called series gap is thereby connected in series to the spark plug.
However, in the conventional gas-filled discharge tube 1 of the above construction, since the gas-filled tube for injecting the gas into the tubular body 2 and the protection terminal 8 are largely protruding from the electrode base 4a, the whole length of the discharge tube 1 becomes substantially long. As a result the plug cap 10 for incorporating the discharge tube 1 therein is forced to undesirably increase in size, so that a minimization of the size of the above ignition system with a series gap becomes difficult. Consequently if an automobile has not a large capacity for mounting engine auxiliary devices or the like, it will become difficult to adopt such an ignition system therein.